1. Field of the Invention
The present invention relates to a solid-state imaging device, such as a charge-coupled device (CCD) image sensor and a complementary metal-oxide semiconductor (CMOS) image sensor, having shading-corrected on-chip lenses on a substrate provided with a plurality of pixels and a method for manufacturing the solid-state imaging device.
2. Description of the Related Art
In video cameras or the like including solid-state imaging devices (refer to, for example, Japanese Unexamined Patent Application Publication No. 6-140609), objective lenses placed in the camera bodies are generally of the inner focus type so that the autofocus speed can be increased. Accordingly, the eye-point distance has recently been considerably reduced from about 100 mm to around 30 mm, and is expected to be further reduced to less than about 15 mm.
FIGS. 9 and 10 are sectional views illustrating known solid-state imaging devices used in systems with different eye-point distances. In the figures, identical components are denoted by the same reference numerals.
As shown in the figures, each of the solid-state imaging devices includes a semiconductor substrate 1, a plurality of light-receiving sections 1a that form a pixel array on the semiconductor substrate 1, and a shading film 2 provided on the pixel array. The shading film 2 is patterned such that each of the light-receiving sections 1a is exposed through an opening formed therein. In addition, an on-chip lens 3 is formed integrally on each of the light-receiving sections 1a. 
Referring to FIG. 9, when the solid-state imaging device having the above-described structure is used in a system having a long eye-point distance, incident light collected by the on-chip lenses 3 reaches the exposed surfaces of the corresponding light-receiving sections 1a even in a peripheral region distant from the center of the pixel array.
However, if the eye-point distance of the system including the known solid state imaging device is reduced, the percentage of light that reaches the light-receiving sections 1a is reduced in the peripheral region of the pixel array, which leads to sensitivity shading. More specifically, as shown in FIG. 10, the on-chip lens 3 positioned directly above the light-receiving section 1a at the periphery of the pixel array can collect only a part of light obliquely incident on the light-receiving section 1a. Therefore, a part of the incident light shown by the hatched area in FIG. 10 is incident on the shading film 2 instead of being received by the light-receiving section 1a. This is called shading, and the degree of shading increases as the eye-point distance is reduced.
Accordingly, methods for correcting shading of the on-chip lenses have been suggested (refer to, for example, Japanese Unexamined Patent Application Publication No. 1-213079).
For example, an on-chip lens array, such as a planar on-chip lens array, is reduced around the effective pixel center by multiplying a reduction scaling factor (for example, 0.999), so that the horizontal displacement between the light-receiving section of each pixel and the corresponding on-chip lens is varied toward the periphery such that amount by which the light-collecting section is shifted from the light-receiving section toward the center is gradually increased.
Due to the above-described shading correction, as shown in FIG. 11, the center of a light-receiving section of the pixel at the periphery of the pixel array is aligned with the center of the corresponding on-chip lens 3 along an optical axis. Thus, the centering error caused by the exit pupil is corrected.
The above-described on-chip lenses are formed by the following method.
That is, first, as shown in FIG. 12A, photoresist 12 including light transmitting material, such as ultraviolet sensitive resin, is arranged on a base substrate 10. Then, as shown in FIG. 12B, ultraviolet light is radiated through a mask 14, so that the photoresist 12 is formed into a matrix pattern corresponding to the pixel array. In this step, transferring is performed with a magnification obtained by multiplying the projection magnification of the exposure apparatus by the above-described scaling factor. Then, as shown in FIG. 12C, a heating process is performed so that the photoresist 12 is formed into hemispherical elements due to the surface tension thereof. This is called a thermal reflow process, and is used in common.